Fixes the regression caused by 7568e1f18e.

runtime/vm/scavenger.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/scavenger.h"
 
 #include "vm/dart.h"
 #include "vm/dart_api_state.h"
 #include "vm/isolate.h"
 #include "vm/lockers.h"
@@ skipping 387 matching lines @@
 }
 
 void Scavenger::Epilogue(Isolate* isolate,
                          SemiSpace* from,
                          bool invoke_api_callbacks) {
   // All objects in the to space have been copied from the from space at this
   // moment.
 
   // Ensure the mutator thread will fail the next allocation. This will force
   // mutator to allocate a new TLAB
-  if (isolate->IsMutatorThreadScheduled()) {
-    Thread* mutator_thread = isolate->mutator_thread();
-    ASSERT(!mutator_thread->HasActiveTLAB());
-  }
+  Thread* mutator_thread = isolate->mutator_thread();
+  ASSERT((mutator_thread == NULL) || (!mutator_thread->HasActiveTLAB()));
 
   double avg_frac = stats_history_.Get(0).PromoCandidatesSuccessFraction();
   if (stats_history_.Size() >= 2) {
     // Previous scavenge is only given half as much weight.
     avg_frac += 0.5 * stats_history_.Get(1).PromoCandidatesSuccessFraction();
     avg_frac /= 1.0 + 0.5;  // Normalize.
   }
   if (avg_frac < (FLAG_early_tenuring_threshold / 100.0)) {
     // Remember the limit to which objects have been copied.
     survivor_end_ = top_;
@@ skipping 287 matching lines @@
       WeakProperty::Clear(cur_weak);
 
       // Advance to next weak property in the queue.
       cur_weak = reinterpret_cast<RawWeakProperty*>(next_weak);
     }
   }
 }
 
 void Scavenger::MakeNewSpaceIterable() const {
   ASSERT(heap_ != NULL);
-  if (heap_->isolate()->IsMutatorThreadScheduled() && !scavenging_) {
-    Thread* mutator_thread = heap_->isolate()->mutator_thread();
+  Thread* mutator_thread = heap_->isolate()->mutator_thread();
+  if (mutator_thread != NULL && !scavenging_) {
     if (mutator_thread->HasActiveTLAB()) {
       ASSERT(mutator_thread->top() <=
              mutator_thread->heap()->new_space()->top());
       heap_->FillRemainingTLAB(mutator_thread);
     }
   }
 }
 
 void Scavenger::VisitObjectPointers(ObjectPointerVisitor* visitor) const {
   MakeNewSpaceIterable();
@@ skipping 60 matching lines @@
   scavenging_ = true;
 
   failed_to_promote_ = false;
 
   PageSpace* page_space = heap_->old_space();
   NoSafepointScope no_safepoints;
 
   int64_t post_safe_point = OS::GetCurrentMonotonicMicros();
   heap_->RecordTime(kSafePoint, post_safe_point - pre_safe_point);
 
-  if (isolate->IsMutatorThreadScheduled()) {
-    Thread* mutator_thread = isolate->mutator_thread();
-    if (mutator_thread->HasActiveTLAB()) {
-      heap_->AbandonRemainingTLAB(mutator_thread);
-    }
+  Thread* mutator_thread = isolate->mutator_thread();

[rmacnak, 2017/08/07 21:29:35]

It looks like isolate->mutator_thread_ is NULL while the mutator is unscheduled,
but we still want to invalidate its TLAB.

Siva, any thoughts on reaching into the ThreadRegistery versus not clearing
isolate->mutator_thread_ ?

[danunez, 2017/08/07 23:09:59]

It looks like isolate->mutator_thread() returns the one cached in
ThreadRegistry. Therefore, we have access to the mutator_thread and its TLAB
until ThreadRegistry itself is destroyed.

+  if ((mutator_thread != NULL) && (mutator_thread->HasActiveTLAB())) {
+    heap_->AbandonRemainingTLAB(mutator_thread);
   }
 
   // TODO(koda): Make verification more compatible with concurrent sweep.
   if (FLAG_verify_before_gc && !FLAG_concurrent_sweep) {
     OS::PrintErr("Verifying before Scavenge...");
     heap_->Verify(kForbidMarked);
     OS::PrintErr(" done.\n");
   }
 
   // Prepare for a scavenge.
@@ skipping 106 matching lines @@
   // if the VM cannot create more pages for these objects.
   ASSERT((UsedInWords() == 0) || failed_to_promote_);
 }
 
 int64_t Scavenger::UsedInWords() const {
   int64_t used_in_words = (top_ - FirstObjectStart()) >> kWordSizeLog2;
   return used_in_words;
 }
 
 }  // namespace dart